Acousto-optic bragg cell

Abstract

An acousto-optic modulator utilizing light diffraction by phased acoustic waves in a birefringent crystal. The wavevector of the resultant acoustic wave is selected so that the tangents to the loci of the wavevectors of the incident and diffracted light are parallel. This provides a large acceptance angle for the acousto-optic modulator. By simultaneously choosing the acoustic wavevector to be tangential to the locus of the diffracted light wavevector, the acousto-optic modulator also achieves increased modulation bandwidth.

What is claimed is: 
     
       1. An acousto-optic modulator for diffracting an incident light beam having an incident wavevector k i  and a first polarization to a diffracted light beam having a diffracted wavevector k d  and a second polarization that is orthogonal to the first polarization, said modulator comprising: a) an optically birefringent medium;   b) means for focusing and passing said incident light beam through said optically birefringent medium; and   c) an acoustical phased array comprising a plurality of acoustic transducers where each of said transducers excites an acoustic wave with a wave vector k a , said plurality of transducers having proper relative phases forms a phased array with an array vector k b , and superposition of all the acoustic waves from said phased array generates a spatially modulated acoustic wave with a resultant wave vector k c  being equal to the vector sum of said acoustic wave vectors k a  and array vector k b , and where the direction of said resultant wave vector k c  is selected such that the tangents to the locus of the incident wave vector k i  and the locus of the diffracted wave vector k d  are substantially parallel.   
     
     
       2. The acousto-optic modulator of claim 1 further comprising means for selecting the direction of said acoustic waves such that said acoustic wave vector k a  is substantially tangential to the locus of the diffracted wave vector k d . 
     
     
       3. The acousto-optic modulator of claim 1 further comprising means for collimating and combining said incident light beam and said diffracted light beam into a single light beam with two different optical frequencies and orthogonal polarizations. 
     
     
       4. The acousto-optic modulator of claim 1 wherein said plurality of acoustic transducers being arranged in a planar array of transducers coupled to said optically birefringent medium, and a means for applying high frequency signals to the transducers, the phase difference between adjacent transducers is 180°. 
     
     
       5. The acousto-optic modulator of claim 1 wherein said plurality of acoustic transducers being arranged in a stepped transducer array blazed at proper angle for exciting a single spatially-modulated acoustic wave. 
     
     
       6. An acousto-optic deflector for diffracting an incident light beam having an incident wave vector k i  to a diffracted light beam having a diffracted wave vector k d , said acousto-optic deflector comprising: a) an acoustically anisotropic medium in which the directions of the acoustic phase velocity and group velocity are generally different;   b) a means for collimating and passing said incident light beam along a selected axis through said acoustically anisotropic medium; and   c) an acoustical phased array comprising a plurality of acoustic transducers where each of said transducers excites an acoustic wave with a wave vector k a , said plurality of transducers having proper relative phases forms a phased array with an array vector k b , and superposition of all the acoustic waves from said phased array generates a spatially modulated acoustic wave with a resultant wavevector k c  being equal to the vector sum of said acoustic wavevectors k a  and said array vector k b , and where the direction of said acoustic waves are selected such that the direction of the acoustic group velocity V g  of said acoustic waves is substantially perpendicular to said axis of incident light.   
     
     
       7. The acousto-optic deflector of claim 6 further comprising means for selecting the direction of said acoustic waves such that said acoustic wave vector k a  is substantially tangential to the locus of the diffracted wave vector k d . 
     
     
       8. The acousto-optic deflector of claim 6 wherein said acoustically anisotropic medium comprises an optically birefringent crystal and the polarization of said diffracted light beam is orthogonal to the polarization of said incident light beam. 
     
     
       9. An integrated acousto-optic modulator for diffracting an incident light beam having an incident wave vector k i  and a first polarization to a diffracted light beam having a diffracted wave vector k d  and a second polarization that is orthogonal to the first polarization, said integrated acousto-optic modulator comprising: a) an optical waveguide formed on the surface of an optically birefringent crystal substrate;   b) a means for coupling said incident light beam into said optical waveguide such that said incident light beam travels through said waveguide; and   c) an acoustical phased array comprising a plurality of inter-digital transducers where each of said transducers excites a surface acoustic wave with a wave vector k a , said plurality of inter-digital transducers having proper relative phases forms a phased array with an array vector k b , and superposition of all the surface acoustic waves from said phased array generates a spatially modulated surface acoustic wave with a resultant wavevector k c  being equal to the vector sum of said acoustic wave vectors k a  and said array vector k b , and where the direction of said resultant wave vector k c  is selected such that the tangents to the locus of the incident wave vector k i  and the locus of the diffracted wave vector k d  are substantially parallel.   
     
     
       10. The integrated acousto-optic modulator of claim 9 further comprising means for selecting the direction of said surface acoustic waves such that said acoustic wave vector k a  is substantially tangential to the locus of the diffracted wave vector k d . 
     
     
       11. The integrated acousto-optic modulator of claim 9 wherein said plurality of inter-digital transducers being arranged in a stepped array of inter-digital transducers blazed at the proper angle for exciting a single spatially-modulated surface acoustic wave.